I don't really support this. If you want a knockback sword, then get it yourself. It is too overpowered, even if it is only knockback 2, because you are able to eliminate whole teams with that. Perhaps have it a low durability, like 3 hits or so, just so you can't spam it. You would need to be more strategical with it.

This is an awful idea
Skywars is about PvP and strategically building bridges to others. NOT getting hit across half the map with some stupid sword or bow someone found in a chest
This would ruin PvP and cause lots of rage -.- Not a very great idea man